Vision impairments such as myopia, hyperopia and astigmatism can be corrected using eyeglasses or contact lenses. Alternatively, they can be corrected with eye surgery. Surgeons have traditionally performed eye surgery using manual surgical tools, such as microkeratomes and forceps. More recently, however, laser ophthalmic surgery has gained popularity with lasers being used in a variety of ways to treat visual disorders.
A surgical laser beam is preferred over manual tools because it can be focused accurately on extremely small amounts of ocular tissue, thereby enhancing precision and reliability of the procedure, as well as improving healing time. Indeed, studies show that more patients achieve an improved level of post-operative visual acuity in the months after surgery with a laser system than with manual tools.
Depending on the procedure, and/or the required visual correction or indication, laser eye surgery may involve one or more types of surgical lasers, including for example, ultraviolet excimer lasers, and near-infrared, ultra-short pulsed lasers that emit radiation in the picosecond or femtosecond range. Non-ultraviolet, ultra-short pulsed lasers emit radiation with pulse durations as short as 10 femtoseconds and as long as 3 nanoseconds, and with a wavelength between 300 nm and 3000 nm. Both ultraviolet and non-ultraviolet ultra-short pulsed lasers are used in the commonly-known LASIK (laser in-situ keratomileusis) procedure that is used to correct refractive errors.
With the LASIK procedure, surgeons typically use a non-ultraviolet, ultra-short pulsed laser to cut a superficial flap in the cornea, which is still attached to epithelial tissue in a hinged area. The surgeon lifts the flap to expose the corneal stroma, which he or she then photoablates with an ultraviolet excimer laser to reshape the cornea. Reshaping the cornea helps correct refractive vision problems such as myopia, hyperopia, and astigmatism. Cornea can also be reshaped using other procedures such as photorefractive keratectomy (“PRK”).
Besides cutting corneal flaps, ultra-short pulsed lasers are used for other types of eye surgery, including for example, performing incisions for corneal implants, performing intrastromal incisions for refractive correction, as well as for incisions for cataract surgery, such as clear corneal incisions that allow access to the lens capsule, capsulotomy that incises the capsular bag for access to the cataractous lens, and incisions in the lens for softening and segmenting the lens so it can be removed from the eye, and replaced with an artificial intraocular lens.
Conventional ultra-short pulse laser systems have been used to cut tissue and to treat many patients. Many of these systems, however, may provide less than ideal results in at least some instances, particularly, in aligning the eye with the laser surgery system's output beam.
Further, conventional laser surgery systems are physically large, heavy, and stationary and as a result, employ a fixed vertical angle of incidence of the output beam. As illustrated in FIG. 8, a conventional laser beam 800 has a vertical angle of incidence along the Z-axis. The XY plane is parallel to a ground surface while the Z-axis is perpendicular to the ground surface. Some of these conventional laser systems are known to incorporate subsystems that move the output point of the laser beam pulse horizontally and vertically while maintaining the same fixed vertical angle of incidence. While some ultra-short pulse laser systems include a treatment arm or head to output a beam that may be adjusted along the X-axis, Y-axis and Z-axis, other systems include a fixed treatment arm. These systems provide only limited adjustability of the laser beam. Hence, the laser beam's angle of incidence is not adjustable in any current system. Rather, all laser surgery systems provide only a fixed vertical angle of incidence, where the output laser beam is always perpendicular to the plane of the floor.
Because of these limitations, the standard procedure has been to adjust the position of a patient's eye relative to the fixed vertical angle of incidence of the beam. Generally, a patient bed is provided for a patient to lie horizontally such that the patient's eye may be maneuvered to intersect perpendicularly with the laser beam. This fixed angle of incidence, however, may pose constraints on patients with abnormal body shapes and conditions, who are unable to lie flat on a patient bed. Examples of these patients include those with scoliosis or other conditions where the back is abnormally bent, and therefore, cannot lie flat. Indeed, in at least some such instances, the patient's back and head may be tilted such that the beam is unable to intersect the eye perpendicularly even if the eye is aligned directly beneath the beam. In some cases, makeshift solutions, such as pillows, are used to contort the patient's body to temporarily (and at times, precariously) align his or her eye with the laser beam. In severe cases, even makeshift solutions are inadequate, meaning that these patients are unable to receive treatment because they cannot be physically aligned with the vertical laser beam 800, as shown in FIG. 8.
Even for the majority of patients with normal spinal curvatures, subtle misalignment may exist as the eye may not be precisely perpendicular to the laser beam. The eye comprises complex optical structures, and misaligning the eye with the surgical treatment apparatus can result in less than ideal placement of incisions in at least some instances.
For all these reasons, it would be desirable to provide improved methods and systems that overcome at least some of the above limitations of the above prior systems and methods.